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Intracellular formation of carbonates by bacteria as a new case of genetically controlled biomineralization
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Edité par CCSD -
International audience. Achromatium oxaliferum, an uncultivated bacterium forming intracellular amorphous calcium carbonates (iACC) was discovered in 1893 and remained a curiosity for a long time. Since 2012, the reported diversity of bacteria forming iACC, including MTB and diverse cyanobacteria has dramatically increased, substantiating a new case of controlled biomineralization in bacteria.They are found in very diverse environments from marine to freshwater, oxic to anoxic environments, soils or thermal water. Inclusions are invariably amorphous, storing huge amounts of Ca and/or other alkaline earth elements. Bacteria can form iACC even in aqueous solutions undersaturated with all CaCO3 phases. Sometimes, these bacteria can be locally abundant. These biocarbonates can have major, trace element and/or isotopic compositions at odd with what is expected for abiotic carbonates precipitated in the same environment. In particular, one cyanobacterium efficiently sequesters the radioactive 226Ra isotope intracellularly, even in Ra-diluted solutions, opening new avenues for the future development of 226Ra bioremediation strategies. The mechanisms involved in the formation of bacterial iACC likely differ among diverse bacteria. Interestingly, a gene family with no homologue of known function was discovered, serving as a good marker of the capability of cyanobacteria to form iACC. Phylogenetic reconstructions indicate that this gene was present in ancestral cyanobacteria with losses in multiple lineages along the evolution of Cyanobacteria. Some recent investigations suggest that the encoded protein may associate with lipids. Last, some recent data show that this biomineralization capability may have been transferred to other phyla.
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